Electrical network and method of transmitting electric currents



Oct. 19 11926. v

. O. J. ZOBEL ELECTRICAL NETWORK AND METHOD oF TRANSMITTING ELECTRIC cURRENTs Filed August 9, 1922 i .3 Sheets-Sheet 1 7. ,M @f w. 79. w.

,w IaI E l INVENToR. BY 0J Zae fawn# ATTORNEY oct. 19, 192e. h 1,603,305

o. J. ZOBEL ELECTRICAL NETwoRxAND METHOD oF TRANSMITTING ELECTRIG cURRENTs Filed August 9, 1922 5 sheets-sheet 2 R ,l

IN V EN TOR.

ATTORNEY 4UNITED STATES PATEN Pstntel bei. 19, 1.928.

A OTTO J. ZOBEL, 0F NEW YORK, Il. yY., ABSIGNOB '.l'O AMEBIGAN TELEPHONE AND TELE- r yolricl-z. y

GRAPH 00mm, A CORPORATION 0I' NEW YORK. g

mc'inrcar. Jstzarwomz Ami nunon or rmsnrr'rma atacan-.Ic cnnnms.

. 'animation and, Augusta, was.l serial no. scarsa.

The principalobject of my invention is to provide a new and improved electrical network whose impedance over a considerable frequency range will be substantially a constant resistance. Another object of my invention is to provide such a network lhaving a given desired attenuation-frequency characteristic. A further object of my invention is to provide an attenuation equalizer fory use 1n carrier currentl signaling. All these and other objects of my invention will be made apparent in the following vspeoificationand claims taken with the aceompanying drawings, in which 'I have disvclosed speclic examples of practice in ac- @cordance with the invention. It will be understood that the invention is defined in the appended claims, and I will now prooeedto describe those examples which I have chosen to present by way of illustration.

Referrin to the drawings Figure 1 is a -vdiagram oA a certain type of network of recurrent like sections with mid-series termination; Figs. 2, 3 and '4 are corresponding diagrams for the same network, but' respectively with mid-shunt, full series and full shunt terminations. Fig. 5 is a dia ram for a lattice type recurrent networ Fig. 6 is a diagram showing one way in which the currents ma be resolved in a section of Fig. 5. Figs. 8, 9 and 10 are, respectively, special case diagrams corresponding to Figs. 1, 2, 3 and v4, but these special cases all have the property -that the characteristic impedance is a constant resistance. Figs. 7a and 8 show'equivalentA desi s for the shunt and series'elements of Figs. 7 and 8 respectively. Figs 11 and 12 are diagrams showing how two impedances an and z2, may be embodied physically, subject to the equation zwem: R2. Fig. 13 is a diagram for graphic computation in connection with Figs. 7 to 10. Fig. 14 shows' a structure having its impedance equivalent to the passive impedance of a certain telephone receiver within a range of from 0 to 3000 cycles per second. Fig. 15 shows how that telephone receiver can be connectedinto a network of constant resistance character 1st1c lmpedance. Flg. 161s a dlagram showmg an attenuation equahzer made 1n accordance with my invention. Figs. 17 and 18 give attenuation characteristics involved 1n connection -with the design of Fig. 16.

In explanation of the term passive impedance as employed above, this refers to the .impedance on the assumption that the receiver dlaphragm is held mechanically agalnst vlbration so that the reaction due to the vibration of the diaphragm introduces no apparent factor in the-impedance across the telephone receiver input terminals.

The type of network shown in Figs. 1 to 4 conslsts of successive alternate series impedances z, the Afirst stage in the investigation of the theory of such recurrent networks, it will here e assumed, as is usual, that the recurrent structure is continued one way to innityl'; this is indicated by the dotted lines to t e rlght. The structure of Fig. 1 begins' at the left with the terminals 11, 12 and a series element whose impedance is half the normal series impedance value, that 1s, 1/221. This ending is called mid-series.

-In Fig. 2 lthe initial terminals 13 and 14 lead at once to a shunt element whose admitvtance is one-half the normal shunt admittance, and accordingly whose impedance` is 'ance is called the mid-series characteristic imfpedance and is designated Km. With re erence to the section 11, 12, 11', 12', the

` following equation will serve for the deter- 4mination of Kms..

The solution of this equation is:

K,',=v zl'zg-l-zlz l(l The impedanceacross the points 13, 14 in Fig. 2 is called the mid-shunt characteristic yson-with Fig. 1 shows that impedance and is designated Km. Comparif Lief-21 QZ The solution is: 'l

From equation 1, it follows that the characteristic lmpedance across 15, 16 in Figs. 3, viz, the full series characteristic impedance, is given by the formula.:

Also the impedance across 17, 18 in Fig. it, the full shunt characteristicimpedance, 1s given by Y A present it is assumed thatA this ligure extends to iniinity from the terminals 19, 20.'

The'impedance across these terminals 19, 2O will be the same as across the points 19', 20', looking to the`right in. both cases.' Designatin this as the lattice type characteristic impe ance K1, we see that the section 19, 20, 19', 20.7 may be treatedl as a 'Wheatstone bridge, the impedance ofthe arm 19', 20

being K1 with respect to an electromotivel force applied across the'tjerminals 19 20. Accordingly, by the well known method for the Wheatstone bridge,.the solution may be found v The' ropagation constant l1 of la recurrent networ such'asshown in F igs.v1 to 5 is dened by the equation:

where I.l is the current in the'gth mesh or section and In.,1 is the current in the v(g-|-1)th mesh or section. I is, m general, a comef" ,special values to z, and z2 in Figs. l to 5,

plex number, and therefore we have:

l"=a+z' (7) where a is called the attenuation constant and is called `t-he phase constant; The

propagation constant I is evidently the same' for Figs. 1, 2, 3 `and 4.

Referring to Fig. 1, and expressing the potential drop across `the points 21,v 22 as equal to the drop acrossy the points 23, 24,

i Formulas 8, 9 and 10 are for Figs. 1, 2,3 and 4, but formula 9 is, neral for any recurrent network. Equations for the propagation constant I` for the lattice type network of Fig. 5 will now be developed. The

`currents in a section of Fig. 5 are resolved into componentsz'l, e', and i, asindicated inl the diagram Fig. 6. The' drop over. the path 19, 19', 20 being the same as directly across 19, 20, and in view of equation 5, we have I From this equation it is readily deduced that er=Iq+1 :u Iq' whence it follows that 22e-2 (19,'. Applying the definition of,l equation 9, it

- Since equation 9 is general, applying to all the figures, and expressing l as a function of u and o, I refer to u and v as the universal variables. p

I shall now proceed to show how, by giving the respective characteristic impedances may I be made equal to a constant resistance in each v v Let the desired constant resistance value be R. Then Figs. 7, 8, 9 and 10 show the respective special case forms assumed by Figs. 1, 2, 3 and 4'. The impedance values designated zu and z2, in these four figures follows that for the lattice type network of. '11o in that they lare to be understood as subject to the relation l It will be seen that the general seriesn impedance z,- of Fig. 1 is represented in Fig. 7 by the impedance of the parallel combination having 2R in one branch and an im# pedance al, in the other branch. This .1mpedance 2 may have any arbitrary design. It may be represented by resistance, inductance or capacity or any` combinatlon of these. However, when a value has been assigned for 2,1, the value of z2, is determined by equation 13. The shunt element z2 of Fig. 1 is seen to be represented in Fig. 7 vby the impedance z2, in. series with the parallel combination of and 221. An equivalent structure for 22 is shown in Fig. 7". .According to the resistance .and reactance values involved, one design the more convenient.

Whatever the physical structure'that gives the impedance all, provided it is composed of lumped elements, it' is possible in practical cases to design a physical structure of lumped elements for 221, so that equation 13 will be satisfied. For example, suppose that al, is embodied in the structure shown in Fig. 11. Then z2, will be given by the structure shown in Fig. 12. It will be seen that there is a complete homology, a series inductance in 2,1, corresponding toy a shunt condenser in z2, and vice versa, these respective inductance and capacity ele-ments being related the equation -:R also a 'shunt or serie l/resistance al, corresponds respectively to #series or shunt resist-ance of reciprocal value times R? in .221.

I shall now proceed to show that the characteristic impedance for Fig. 7 reduces to R.

Comparison between Fig. 1 and Fig. 7 shows that l 41R Z, '2" 1 @T-fri and z.- 1 +22. y(14) Substituting these values in equation 1 and expressing z2, in terms of al, bymeans of equation 13, we get Kms=R.

By a similar procedure it may be shown that the respective characteristic im edances -for Figs. 8, 9 and 10 each reduce to l Referring to Fig. 5, let z, and z2 take therespective values a1, and zu, specially related as in equationl.4 Then by equation 5 we get at once that K1=R, thus putting Fig. 5-in the same class with Figs. 7, 8, 9 and 10 pedance which is 'the constant resistance R, independent of frequency.

or the other may be all have a characteristic im- Substituting from equations 13 and 14 in that +iva R (15) 1+@ Similarly for .the cases represented by Figs. 8, 9 and 10, the universal variables u, and 'v are found to be the same andare given by equation 15.-

Remembering that the v'important func. tions of a recurrent network are its characteristic impedance and. its propagation 'constant, we see that these are all comprised in the foregoing discussion. For each of Figs. 7, 8, 9 and 10 and also Fig.- 5 the equation 10, and reducing, we get for Fig. 7

characteristic limpedance is R, provided'the I elemental impedances ,au and 22,/ satisfy equation 13. The propagation constant I is given in general .by equation 9, which expresses F as a function of the universal variablesu and lv. -These variables are given for Figs. 7, 8, 9 and 10 in equation l5 and for Fig. 5 'in equation 16.

Thus in Figs. 7, 8, 9,10 and 5 We ha available tive different designs from which to choose in setting up a recurrent network of constant resistance characteristic impedance. Moreover, each of these five types is general in that it comprises two impedances al, and 22 one of which -may be given any value We please. Thus it -will be seen that in the designl of networks to suit required .v

conditions, considerable flexibility is afforded. f

It will be recalled that early in this specification the condition was laid4 down that the recurrent netwprks under consideration .should extend from the initial terminals to infinity. It will now be seen that the impedance and current relations will be un- "altered, if, at an appropriate point corresponding tothe initial point, the system is closed by a resistance R. Thus, in Fig. 7, which has mid-series initial termination at 25, 26, if at any mid-series points such as 25', 26ythe switches are thrown, theeect at the sending points 2,6 will be unalthrown. These networks may be used in any situaiis tei-ed and the currents in the finite sequence.

tion where the termination is' a constant re- Y.

they iigemore simple in structure andthere-V fore .me economical to build and maintain,l

but resymmetry in opposite directions is desil the mid-series and mid-shunt end- Figs. 7 and 8 respectively and the 'symme rical structure of Fig. 5 all have an advantage over Figs. 9 and 10. p

It has been shown 1n my applicatlon,

` Serial. No.437,527,led January 15, 1921 that ina recurrent network or wave filter I term M-types to designate such .substituted sections which do notv alter the characteristic impedance, but which do change the atduced that of the 'kind shown in Figs. 1 to 5, interior sections can be replaced by sections ofal tered design (subject to certain conditions) without affecting thecharacteristic impedance. With respect to a given design of sections 'as in Figs. 1 to-4, I have used the tenuation properties..v Such M-type substitutions may be made in any one of the networks of Figs. 7, 8, 9 and 10, and correspondingsubstitutions of what I call an L- type may be made in the sections of Fig. 5.

In connection .with any one" of the net-A works of Figs.` 7, 8, 9 and 10, 1t may be* convenient to employ a graphic method of computation, which I will Aoutline briefly with reference to Fig. 13. From equations 8, 13 and 14, or directly from Figs. 47A to 10, it may' readily be de- R Substituting fromA equation 18 ain equation :Tn-+5311 (18) l 17 and also relying on equation 7, the result is obtained that line OY 4-s the axis of ordinates and on it a scale of values `for m1, is laid off. VSince r11 represents reslstance, it 1s usually positive, and kin absolute value the right-hand member of equation V19 will be the same whether wn is ositive -or negative. Hence, .the quadrant s own in Fig. 13 will be sui- "R51 determined by cient for all cases. Draw AP to the point and au. The lengt AP represents e a and the angle OAP in circular measure gives the vvalue y of its sign corresponding to the sign of wn. p

particular values ofrn 'R' of that sectioni'offFi A set of circles may" be` drawn from O as center, and each one labelled with the corresponding value for a, then, by means of a. diagram such as Fig.' 13, the attenuation constant a can be immediately determined.

when the components of R are known.

AAlso the phase constant can be quickly determined as the circular measure of the angle lOAI). l Correspondingv formulas and charts for the lattice type network of Fig. 5'can also be deduced and a chart prepared for graphic solution. A Y

To illustrate a use for-my improved network, suppose that we have a piece of apparatus vwhose impedance f compriss reactance and varies overa certain frequency range, whereas it is desired that the introduction of the-a paratus in a reactanceless circuit shall not introduce reactancenor introduce any variable impedance. By the use of my invention this piece of apparatus may be introduced as an element of one or more sections of a network such as shown inFigs. 7, 8, 9, 10 or 5. The design of the network comprising this piece of. apparatus will be such as to make the characteristic impedance a constant resistance. then the network so designed can be put in the circuit without introducing any reactance or any impedance that varies with frequency.

For example, the passivel impedance of a certain telephone receiver, on being measured over the voice frequency range, was found to have the following values:

Erequency (cycles), Impedance (ohms) By trial it wasV found that this impedance could' be represented approximately by the Y network shown in Fig. 14. The constants of this network were chosen` to giveit the exact impedance of ther` telephone receiver T at 600 cycles and at 2000 cycles and itwasthen found to differ by less than 3.5% at all frequencies up/to' 2,500 cycles l. andloyV less l than 5.5% at3,000jcycles.

Let the impedance ofthe between the points 29,l and -30',of` Fig.l 14: vbe

taken as 21, of the'section327, '28.271 28.. of

Fig. V1Y0, the switches i297 ,'v 28"fbeing lthrown to closev the'section on R," andlletzthe-.resistance-.R1 of Fig. r14be ypart ofthe terminal But when they are thrownas shown in .28 of the network of'Fig. 15, of which network the receiver T is an element, the impedance is substantially a constant resistance. I' V For another illustration of a' use for my invention, I will 'explain the design of an attenuation equalizer to be interposed be-A tween a line and 'a repeater. Each repeater Rp, and R112 in Fig. 16 is assumed to have constant resistance R, and its is desired to interpose attenuation equalzing networks N, and N2 between these repeaters and the line 31, so that the attenuation to the repeaters shall be constant and the impedance of the networks combined with the respective re- D2, as the case may be. All the attenuations l 0f Fig.. 17 are expressed per mile of the v f Havin peaters shall be the same as of the repeaters alone.

The line 31 with which connection is made is assumed for the purpose of this example to be a certain line 150 miles long for which the attenuation characteristics have been determined experimentally, as shown in Fig. 17. It will bev seen that the attenuation increases with frequency, but at a rate depending largely on weather con.- ditions. The curve D is chosen as the basis for design, this curve giving the average attenuation for this 150 mile line under wct weather conditions.

Wave lters F, and F2 are connected to the line 31 as shown in Fig. 16 to separate into respective channels the two frequency ranges, one extending from 6.6 to 19 kilocycles andthe other extending from 21 to,

30 kilocycles. The line 31 attenuates the currents as shown by the characteristic D in Fig. 17 It is desired that the attenuation v up to thel repeater input terminalsshall be constant, as `shown, for example, by thev characteristics D,", D2', therefore the networks N1 and N2should have attenuatlon characteristics like D, and D2, so that at all vfrequencies within the respective ranges the ordinates of D1 and D2 shall be obtained by summing the ordinates of D and D, or

line, hence the ordinates of D, and D2 must be multiplied b 150 to give the desired attenuations in t e networks N, and N2.

determined in the characteristics D', and 2 how the networks N, and N2 are desired to function, we assume that the net-` work lwill be a single section of Fig. 10, namely the section 27, 28, 27', 28. The glven constant resistance characteristic impedanc'e of the repeater becomes element R of the network of Fig. 10, on which the switches 27',y 28 are assumed to be closed.

To embody 5 in an appropriate physical structure to realize the attenuation characteristic D, or D2, we are guided by-equation 17, (taking the absolute values of its members) and by trial4 the network desi nated z at the top of Fig. 16 is found to e appropriate. Then b the aid of equation 13 the combination' o elements designated z2, in Fig. 16 is obtained to represent the like designated element in Fig. 10.

For greater. accuracy account is taken of the dissipation in the inductance coils, `and this is treated as a small equivalent resistance.

As to thev particular values to be assigned to 'the resistance and reactance elements that make up the impedances 2 and z2, of Fig. 16, these ma be determined by assuming a number o points on the characterfistic D, or D2 of Fig. 17 corresponding to the number of available arameters and then making the attenuation c aracteristic for the 'network N, or N2 pass through those points. l In this way a very close approximation may` by the curves in Fig.

.less the currents at the repeater input terminals are of constant attenuation for all frequencies within their respective ranges. The attenuation equalizing networks N, and N2 give high attenuation when the line atf tenuation is low and vice versa, so that as' combined with| the line theyv give a constant attenuation. At the same time this 'result is secured without introducing imedance irregularites and consequent reection effects. Thev impedance looking from the line 31 into the network N, vhas the same constant resistance value aty all frequencies as when looking into the repeater at its input terminals.

The same 2 and z2, might be used in a single section of the networks of Figs. 7, 8 and 9 to et N, and N2. The same attenuations an would result. Fig. 10 gives .an economical design however.

4I claim: i

1. A network comprising a series network in which there is, an impedance of general value 2,-, where 2 is any function of frequency, and also comprising a shu'..t netconstant resistance impedancesv sol R is a constant, said network .as a` whole' having constant resistance R over aiange of frequencies at its input terminals.

2. A network whose characteristic impedance.over a ran of frequencies is the com" stant resistance said network comprising at least one section having a `series lmpedance element 2 and a shunt impedance. element R-l-as21 subject to the -equationv zn.z21=R, said network having a resistance V R across the output 'terminals of vthe last section.

. A network having a pair of input ter'- minals and a pair of output terminals, andimpedance element R--l-z2'1 subject to f the equation an.z2,=R2, said network also having a constant resistance R across its output terminals and its elements being so proportioned and arranged that the characteristic impedance .'at the input terminals overv a range of frequency is R.

5. A network havingapair of input ter. minals and a pair of output terminals, said network comprising at least one lof several like sections between said pairs of terminals with a constant resistance R across the out put terminals,- each such section comprising aseries network in which there is a general impedance zn'and also comprising a shuntnetwork in whic there is another impedance an related by the equation znznzRz, the input impedance of thev network with; the said constant resistance R across itsoutput terminals being a constant resistance of the same value.

6. An attenuationk equalizer between a termimng ipo-8,305

source of electrom'otive force a constant resistance B conslsting of an interposed network comprlsing twoimpedances- 2 and 2 such .that fz,'1fz`=R*,` one impedance 2 b eing designed to satisfythe equation where is Aa propagation constant whose `attenuation component iscom lementary to` one of` saidy impedances being in series in relation to said. source and said constant resistance R, and

the attenuation to be equalize the otherrof said two impedances being in shunt to said source and resistance.

7. The method of combining adevice of general impedance value in a network that shall have a constant resistance R over a desired frequency range which consists in deacteristic impedance zu as saidv device .over said 'frequency range, then ormin a structure having impedance zu such t at 21122,:R2 and combining said deviceand said structure in a network with zu as a se` ries component and z2, as a shunt component.

8. The method of 4equalizing the attenuation of a current from a source of E. M. F.

to a constantresistance R without' altering the impedance presented A to said source, which consists in interposing a suitable network comprising a general impedance 21 designed by trial to satisfy the equation where I is the propagation constant whose attenuation component is complementary to l the attenuation tov be ualized, said net work also comprising aniher impedance z2, related by the equationznzz1=R Y In testimony whereof, I have signed my name to this August, 1922.

. OTTO J. zoBEL.

by trial an impedance `struc-A ture that shall have the. same char-- specification 8th day of 

